Hydrostatic holding devices have been used for a number of years to hold workpieces which are to be machined or ground. Also, U.S. Pat. No. 5,516,243 discloses a hydrostatic holding device constructed to hold a reamer chuck within a tool spindle and also a hydrostatic holding device constructed to releasably hold a cutting tool within the reamer. Both of these hydrostatic holding devices utilize a sleeve which contracts under hydraulic fluid pressure to firmly hold the object within the sleeve. These sleeves are generally cylindrical and are constructed to receive a cylindrical shank of a tool or tool holder.
Other tool holder devices utilize a machine spindle having a tapered recess into which a complementary shaped chuck or machine tool is inserted. To accurately and concentrically align the chuck with the machine spindle, each tapered portion must be exactly complementary in shape to provide substantially full engagement between the chuck and the machine spindle along the entire length of the tapered portions. Further, to ensure a concentric fit between the chuck and machine spindle it is desirable that the full engagement between the two occur simultaneously with the mating of transverse opposed flat faces of the spindle and chuck. It is extremely difficult to accurately manufacture the tapered portions of both the chuck and the machine spindle to provide this precise engagement needed to ensure a concentric and accurate fit. Further, during use the tapered portions become worn which further degrades the engagement of the spindle and chuck.